Bondhead lead clamp apparatus and method

ABSTRACT

A method of forming improved wire bonds between the contact pads on semiconductor devices and individual lead frame fingers of a lead frame. The method includes the use of an individual independent lead finger clamp during the wire bonding process to provide increased stability of the individual lead finger for improved bonding. If desired, the method also provides for the use of a conventional fixed clamp for the lead fingers during the wire bonding process in addition to the individual independent lead finger clamp during the wire bonding process to provide increased stability of the individual lead finger for improved bonding and also provides for the replacement of the fixed clamp with another, or second, independent clamp.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of application Ser. No.09/941,019, filed Aug. 28, 2001, pending, which is a continuation ofapplication Ser. No. 09/407,483, filed Sep. 28, 1999, now U.S. Pat. No.6,325,275, issued Dec. 4, 2001, which is a continuation of applicationSer. No. 08/865,911, filed May 30, 1997, now U.S. Pat. No. 6,000,599,issued Dec. 14, 1999, which is a continuation of application Ser. No.08/597,616, filed Feb. 6, 1996, now U.S. Pat. No. 5,647,528, issued Jul.15, 1997.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention is related to forming wire bonds betweenthe contact pads on semiconductor devices and individual lead framefingers of a lead frame.

[0004] More specifically, the present invention is related to theapparatus and method of forming improved wire bonds between the contactpads on semiconductor devices and individual lead frame fingers of alead frame using one or more independently actuated bondhead lead clampsduring the bonding process.

[0005] 2. State of the Art

[0006] Well known types of semiconductor chip devices are connected to acomponent known as lead frames and subsequently encapsulated in plasticfor use in a wide variety of applications. The lead frame is typicallyformed from a single continuous sheet of metal, typically by metalstamping operations. The lead frame includes an outer supporting frame,a central semiconductor chip supporting pad and a plurality of leadfingers, each lead finger having, in turn, a terminal bonding portionnear the central chip supporting pad. Ultimately, the outer supportingframe of the lead frame is removed after the wire bonds between thecontact pads of the semiconductor chip device and the lead fingers aremade.

[0007] Since the lead frames are formed continuously using stampingoperations, they are typically continuously rolled on a suitable reeland provided for use. Such reeling operations of the lead frames causethe lead frames to have induced deformations therein leading to leadframes exhibiting longitudinal curvature and transverse curvature. Suchlead frame curvature and any attendant deformation of the lead framecause problems in the formation of reliable wire bonds with the contactpads of semiconductor devices and the individual lead fingers of thelead frame, particularly, when the size of the semiconductor isdecreased, the number of contacts pads on the semiconductor device isincreased, and the number of lead fingers on the lead frame isincreased.

[0008] Typical apparatus and methods for forming the wire bonds betweenthe contact pads on semiconductor devices and the lead fingers of leadframes are illustrated in U.S. Pat. Nos. 4,361,261, 4,527,730,4,600,138, 4,653,681, 4,765,531, and 5,465,899. However, such apparatusand methods do not address the problem of deformed lead frames and theireffect on the wire bonds.

[0009] Typically, the deformation of the lead frames and its effect onthe quality of wire bonds have been dealt with through the use of clampson portions of the lead frames during the wire bonding operation. InU.S. Pat. No. 4,434,347, a circular fixed clamp is used to retain thelead fingers of the lead frame during the wire bonding operation. Aspring loaded electrode is used to heat the end of the lead finger tohelp improve bonding of the wire.

[0010] In U.S. Pat. No. 5,322,207, a fixed clamp is used to retain thelead frame during the automated wire bonding process for connecting thebond pads of a semiconductor device to lead fingers of a lead frame.

[0011] In U.S. Pat. No. 5,307,978, a fixed clamp is illustrated for usein an apparatus and method for orienting bonding sites of a lead framehaving a plurality of bonding sites.

[0012] In U.S. Pat. No. 5,035,034, a hold-down clamp having amulti-fingered interchangeable insert for wire bonding semiconductorlead frames is illustrated. The clamp insert 21 includes a plurality ofindividual fingers 22 to be used to bias a lead finger of a lead framein the wire bonding process to provide a better wire bond.

[0013] In U.S. Pat. No. 3,685,137, jaws 26 and 28 of a lead frame clampare used to force the lead fingers of a lead frame into a fixed positionduring the wire bonding process.

[0014] In U.S. Pat. No. 4,821,945, a method and apparatus for the singlelead automated clamping and bonding of lead fingers of lead frames areillustrated. However, such apparatus and method are used to replace thefixed clamp during such wire bonding. Additionally, the individual clampis concentrically located with respect to the wire bonding apparatus andmust rotate therearound during wire bonding operations.

[0015] While such prior art apparatus and methods have been directed inattempting to solve the problems of forming reliable wire bonds betweenthe contact pads of semiconductor devices and lead fingers of leadframes, they have not been as successful as envisioned.

[0016] The present invention is directed to an improved wire bondingapparatus and method for forming such wire bonds.

SUMMARY OF THE INVENTION

[0017] The present invention is related to the apparatus and method offorming improved wire bonds between the contact pads on semiconductordevices and individual lead frame fingers of a lead frame. The presentinvention includes the use of an individual independent lead fingerclamp during the wire bonding process to provide increased stability ofthe individual lead finger for improved bonding. If desired, the presentinvention also provides for the use of a conventional fixed clamp forthe lead fingers during the wire bonding process in addition to theindividual independent lead finger clamp to provide increased stabilityof the individual lead finger for improved bonding. The presentinvention also contemplates the replacement of the fixed clamp withanother, or second, independent clamp in addition to the firstindividual independent lead finger clamp during the wire bondingprocess.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0018] The present invention will be better understood when thedescription of the invention is taken in conjunction with the drawingswherein:

[0019]FIG. 1 is a perspective view of the present invention used in awire bonding process.

[0020]FIG. 2 is a perspective view of a lead-over-chip semiconductordevice having the bond pads thereof connected to the lead fingers of alead frame.

[0021]FIG. 3 is a side view of the present invention used in the wirebonding of a semiconductor chip arrangement.

[0022]FIG. 4 is a perspective view of a second alternative type ofindependent lead clamp of the present invention.

[0023]FIG. 5 is a perspective view of a third alternative type ofindependent lead clamp of the present invention.

[0024]FIG. 6 is a perspective view of the use of two independent leadclamps of the present invention in a wire bonding operation with a leadfinger of a lead frame.

DETAILED DESCRIPTION OF THE INVENTION

[0025] Referring to drawing FIG. 1, a semiconductor chip (die) 10 isshown being supported by the paddle 12 of a lead frame. A heat block 20is used to heat the paddle 12, die 10, and lead fingers 14 during thewire bonding process. As shown, a suitable wire 16 has one end thereof17 bonded to a bond pad of the die 10. The wire 16 may be of anysuitable type for connection and bonding purposes, such as gold, goldalloy, aluminum, aluminum alloy, etc. The other end 18 of the wire 16 isshown being bonded to the end 15 of a lead finger 14 of the lead frameby a suitable bonding apparatus 26. The bonding apparatus 26 may be ofany suitable type well known in the bonding area, such as a taillessthermosonic or ultrasonic capillary type bonding apparatus whichdispenses wire during the bonding process. As previously stated, thelead finger 14 is in contact with the heat block 20 to heat the leadfinger 14 to a suitable temperature for the bonding operation to helpinsure a satisfactory wire bond. If desired, in the wire bondingoperation, further shown in contact with lead finger 14 is a portion ofa conventional clamp 22 used to clamp portions of the lead frame duringsuch bonding operations. The clamp 22 may be of any well known suitabletype, such as those described hereinbefore, and is generic in shape.Further shown in drawing FIG. 1 is independently actuated lead clamp 24used in place of or in addition to the conventional clamp 22 to maintainthe lead finger 14 in position during the bonding process. Theindependent clamp 24 helps insure that the lead finger is in contactwith the heat block 20 during the bonding process and helps minimize anydeflection of the end 15 of the lead finger 14 so that the bondingapparatus 26 accurately, precisely contacts the end 15 to provide thedesired wire bond. The action of independent clamp 24, and if desiredthe additional use of fixed clamp 22, provides improved clamping of alead finger 14 during the wire bonding process as well as insures thatthe lead finger 14 is in intimate contact with the heat block 20 foreffectiveness.

[0026] During the wire bonding process, it is desirable for the heatblock to be heated to substantially 230 degrees Centigrade. Although theheat block may be any suitable temperature during the bonding operation,the heat block 20 temperature should not exceed 300 degrees Centigradeto prevent thermal damage to the die 10. It is further preferred thatthe bond of the end 18 of the wire 16 made to the end 15 of the leadfinger 14 be made at a temperature of substantially 190 degreesCentigrade for bonding effectiveness. It is also preferred that thebonding apparatus exert a bonding force of substantially 50 to 100 gramswhen bonding the end 18 of the wire 16 to the end 15 of lead finger 14for effective bond formation of the wire 16 to lead finger 14.

[0027] The independent clamp 24 may be of any suitable shape for use inindependently clamping the lead finger 14, in place of the use ofconventional fixed clamp 22, such as square, semicircular, rectangular,arcuate, etc. Also, as shown, the independent clamp 24 may beresiliently mounted through the use of a shoulder 50 thereon abutting aspring 52 to control the amount of the force exerted on any lead finger14 during the wire bonding operation. If desired, the independent clamp24 may include insulation or cushioning 25 on the end thereof. Theindependent clamp 24 is actuated independently of bonding apparatus 26and has the capability of independent movement along the x-axis, y-axisand z-axis with respect to the bonding apparatus 26. The independentclamp 24 is also free to move about the bonding apparatus 26 and thecentral axis of the die 10 so that any lead finger 14 that is to beconnected to bond pads on the die 10, regardless of location, may beaccommodated. The independent clamp 24 does not need to be, andpreferably is not, concentrically centered about the bonding apparatus26 so that it will not interfere with the operation thereof. Any desirednumber of independent clamps 24 may be used about the bonding apparatusto minimize the amount of movement of the independent clamp 24 betweenwire bonding operations. The independent clamps 24 may be located inquadrants about the die 10, or in any manner as desired.

[0028] Referring to drawing FIG. 2, a lead over chip configuration usingthe present invention is shown. The lead fingers 14 are located over thechip (die) 10 for wire bonding thereto. In such a configuration, thelead fingers 14 are secured to the die 10 by insulating adhesive strips30. During the bond operation, one or more of the independent clamp 24clamps the end 15 of lead finger 14 prior to the bonding of a wire 16thereto by one or more of the bonding apparatus 26. The independentclamp 24 applies sufficient pressure to the end 15 of the lead finger 14to compress the insulating adhesive strips 30 to insure a satisfactorybond between the end of any wire 16 and the end 15 of the lead finger14.

[0029] Referring to drawing FIG. 3, a die 10 is shown having a pluralityof wires 16 bonded thereto. As shown, one or more of the independentclamps 24 contacts the end 15 of lead finger 14 aft of the area of thewire end 18 to the lead finger 14. The bonds of the wire end 18 to theend 15 of the lead finger 14 are typically a wedge type wire bond,although a ball bond may be made if desired. As shown, the heat block 20is in contact with the paddle 12 of the lead frame and the lead fingers14.

[0030] Referring to drawing FIG. 4, a portion of a lead finger 14 isshown in conjunction with a bonding apparatus 26 and modifiedindependent lead clamp 22′. The independent lead clamp 22′ is formedhaving a modified end or foot 23 thereon to provide a larger clampingarea of the clamp 22′ on the end 15 of the lead finger 14 during bondingoperations. The modified end or foot 23 is substantially the same widthas the lead finger 14 and may be mounted to have articulated movementabout the end of the independent clamp 22′ such as using a pin 125extending through suitable apertures in a pair of ears 27 attached tothe foot 23 and the end of the modified independent clamp 22′ forillustration purposes.

[0031] Referring to drawing FIG. 5, an independent clamp 22′ is shownhaving a modified end or foot 23′ located on the end thereof. The end orfoot 23′ may be integrally attached to the clamp 22′ or may have anarticulated mounting arrangement, such as shown in drawing FIG. 4. Inthis instance, the modified end or foot 23′ is generally semicircular,or arcuate, in configuration so as to engage a large portion of the end15 of the lead finger 14 surrounding the bonding apparatus 26 during thewire bonding operation to hold the end 15 in position.

[0032] Referring to drawing FIG. 6, the independent clamp 24 is shown inrelation to the bonding apparatus 26 on the end 15 of a lead finger 14as well as further being shown in relation to a second independentlyactuated clamp 150 located thereon during wire bonding operations. Thesecond independently actuated clamp 150 may be of any suitable type andstructure such as described and illustrated hereinbefore. The clamp 24and second clamp 150 may be actuated independently of each other andindependently of the bonding apparatus 26 as described and illustratedhereinbefore.

METHOD OF BONDING

[0033] Referring to drawing FIGS. 1 through 3, in the method of thepresent invention, a die 10 is positioned within the bonding area of thebonding apparatus 26. If desired, for use in addition to an individualindependent clamp 24, a conventional clamp 22 serves to help straightenthe lead frame and position the lead fingers 14 during subsequentbonding operations. Next, the die 10 and the lead finger 14 are heatedto the desired temperature before bonding operations by the heater block20. At this time, the independent clamp 24 is engaged, moved to theappropriate lead finger 14 which is to have a wire bonded thereto, andthe clamp 24 actuated to clamp the end 15 of the lead finger 14 againstthe heat block 20 or the adhesive strip 30. The wire bonding apparatus26 is then actuated to form a wire bond on end 17 of wire 16 to anappropriate bond pad on die 10. After the formation of the bond of end17 of wire 16 to the bond pad of die 10, the bonding apparatus is movedto appropriate end 15 of lead finger 14 for the formation of a suitablewire bond thereto by end 18 of wire 16. After the formation of the bondof the end 18 of wire 16 to the end 15 of lead finger 14, theindependent clamp 24 and the bonding apparatus are actuated tosubstantially simultaneously remove the clamp 24 and the bondingapparatus 26 from the end 15 of the lead finger 14. Alternately, thebonding apparatus 26 is actuated to remove the apparatus from the bondlocation at the end 15 of the lead finger 14 either prior to or afterthe removal of the independent clamp 24 from a lead finger 14. Duringthe removal of the bonding apparatus 26 from the end 15 of the leadfinger 14, if used in addition to the independent clamp 24, aconventional clamp 22, if in contact with a lead finger 14, supplies thenecessary force to retain the finger 14 in position relative to otherlead fingers located around die 10, both bonded and unbonded. Aspreviously stated, it is not necessary for the independent clamp 24 toremain in contact with the end 15 of lead finger 14 during the removalof the bonding apparatus 26 therefrom. After the wire 16 has been bondedto the desired bond pad of die 10 and end 15 of lead finger 14, theprocess is repeated until all desired wire bonds between lead fingers 14and bond pads of die 10 are completed.

[0034] If desired to have additional clamping of the lead finger 14,either a fixed clamp 22 and/or a second independent clamp 150 may beused with the bonding apparatus 26. The second independent clamp 150 maybe actuated and moved from the lead finger 14 with, before, or after theremoval of the bonding apparatus 26 from the lead finger 14.

[0035] It will be understood that the present invention may havechanges, additions, deletions modifications, and sequence of operationwhich fall within the scope of the invention. For instance, the fixedclamp may be eliminated and a second independent clamp used in itsplace.

What is claimed is:
 1. A wire bonding method for bonding a portion of awire to a portion of a lead finger of a lead frame using a movable clampcomprising: providing an independently movable clamp comprising a clampmovable in at least one x-axis direction, at least one y-axis direction,and at least one z-axis direction; positioning said independentlymovable clamp over a portion of said at least one lead finger formaintaining said at least one lead finger in position for attaching ofat least a portion of said wire thereto; and providing an apparatus forbonding a portion of said wire to a portion of said at least one leadfinger.
 2. The method of claim 1, further comprising: actuating saidapparatus for bonding a portion of said wire to said lead finger.
 3. Themethod of claim 2, further comprising: disengaging said independentlymovable clamp from said portion of at least one said lead finger beforeremoval of said apparatus from said at least one lead finger.
 4. Themethod of claim 1, wherein said independently movable clamp comprises aresiliently mounted clamp.
 5. A wire bonding method for bonding aportion of a wire to a portion of a lead finger of a lead frame using afist clamp and an independently movable clamp comprising: positioning afirst clamp over a portion of said lead finger for maintaining said leadfinger in a position during said bonding a portion of said wire thereto,the first clamp comprising a clamp movable in at least one x-axisdirection, at least one y-axis direction, and at least one z-axisdirection; positioning an independent clamp over another portion of saidlead finger for retaining said lead finger in said position during saidbonding of said wire thereto; and providing an apparatus for bondingsaid portion of said wire to a portion of said lead finger.
 6. Themethod of claim 5, further comprising: actuating said apparatus forbonding a portion of said wire to a portion of said lead finger.
 7. Themethod of claim 6, further comprising: removing said independent clampfrom engagement with said portion of said lead finger before removal ofsaid apparatus from said lead finger.
 8. The method of claim 5, whereinsaid independent clamp comprises a resiliently mounted clamp.
 9. A wirebonding method for bonding at least a portion of a wire to a portion ofa lead finger of a lead frame using a plurality of clamps comprising:positioning a first independent clamp over a portion of said lead fingerfor retaining said lead finger bor bonding a portion of said wirethereto, said first independent clamp movable in at least one x-axisdirection, at least one y-axis direction, and at least one z-axisdirection; positioning a second independent clamp over another portionof said at least one lead finger for restraining said lead finger insaid position for said bonding of said wire thereto, the secondindependent clamp movable in said at least one x-axis direction, said atleast one y-axis direction, and said at least one z-axis direction; andproviding an apparatus for bonding a portion of said one wire to aportion of said lead finger.
 10. The method of claim 9, furthercomprising: actuating said apparatus for bonding a portion of said wireto a portion of said lead finger.
 11. The method of claim 10, furthercomprising: removing said second independent clamp from said portion ofsaid lead finger before removal of said apparatus from said lead finger.12. The method of claim 9, wherein said second independent clampcomprises a clamp for positioning between said first independent clampand an end of said lead finger.
 13. The method of claim 9, wherein saidfirst independent clamp and said second independent clamp each comprisean independently movable clamp with respect to the other clamp and saidlead finger.